An optically pumped semiconductor device is disclosed for example in U.S. patent application Ser. No. 09/824,086, which describes an optically pumped surface emitting semiconductor device with a radiation-generating quantum well structure and with a pump radiation source for optically pumping the quantum well structure, the quantum well structure and the pump radiation source being grown epitaxially on a common substrate.
With optically pumped semiconductor devices of this type, efficient operation requires precise coupling of the pump radiation into the quantum well structure. What is advantageous in this respect is a lateral delimitation of the pump radiation source which restricts the generation of the pump radiation to a region from which the pump radiation can be coupled into the quantum well structure as completely as possible.
If the quantum well structure and the pump radiation source are arranged at a distance from one another, the guiding of the pump radiation from the pump radiation source to the quantum well structure by means of a waveguide may be advantageous. For this purpose, it is possible to use, by way of example, waveguides in which the propagation of the pump radiation is defined by index guiding. Furthermore, it is possible to use index guiding for the lateral delimitation of the pump radiation source. Total reflection constitutes a special case of index guiding in the context of geometrical optics.
Pump lasers, in particular, are suitable as a pump radiation source, the wavelength of which pump lasers can be coordinated exactly with the optimum pump wavelength. A lateral delimitation, in particular of the laser resonator, to a width that is advantageous for coupling into the quantum well structure is likewise expedient in this case.
However, for example in the case of waveguide structures based on index guiding, there is the risk of the index guiding being disturbed on account of inhomogeneities of the waveguide interfaces or deviations from a predetermined ideal waveguide interface, which may be dictated by production, for example, with the result that radiation can exit from the waveguide. This may result in pump radiation losses which may lead to an impairment of the efficiency of the optically pumped semiconductor device or a reduction of the optical output power.
In the case of semiconductor lasers, so-called index guiding and also so-called gain guiding are known for the lateral delimitation of the resonator. In this case, the refractive index or the gain is varied in the lateral direction in such a way that the laser radiation field is generated or amplified only in a strip-like region of predetermined width. As a rule, however, such structures with index or gain guiding are only suitable for rectilinear resonators.
The abovementioned problems are aggravated further if the pump radiation source, in particular in the form of a pump laser, is embodied in angled or curved fashion. Such angled or curved shaping may be advantageous, for example, if a plurality of pump radiation sources pump the quantum well structure and rectilinear feeding of the pump radiation to the quantum well structure is not possible—for example for space reasons. In this case, radiation losses may occur in particular in the region where a waveguide or a pump radiation source is angled or curved, which radiation losses adversely affect the efficiency of the component.
As an alternative to waveguides exhibiting total reflection, it is known to use so-called photonic band structure elements. These elements have a one-dimensionally, two-dimensionally or three-dimensionally lattice-like arrangement of materials having a different refractive index, the lattice constants being chosen in such a way as to produce a band structure with a band gap for electromagnetic waves. The band structure of such a lattice-like arrangement is in certain respects comparable with the band structure of a semiconductor crystal lattice for the associated electron wave functions: in both the photonic band structure element and the semiconductor crystal lattice, the periodicity of the surrounding lattice leads to a relationship between the wave vector and the associated energy with a plurality of (quasi-) continuous regions, the so-called bands, which are separated from one another by so-called forbidden regions or band gaps. Wave functions or electromagnetic waves whose energy lies in the band gap are not capable of propagating within the lattice. In contrast to a crystal lattice, in the case of a photonic band structure element, the lattice-like arrangement is not formed by individual atoms, but rather by a macroscopic arrangement of dielectric media.
An angled optical waveguide with a photonic band structure element which is based on this principle is known for example from U.S. Pat. No. 6,134,369.